Composition for use in a transparent and electrically conductive film and a method for making the film

ABSTRACT

An object of the present invention is to provide a composition for use in a formation of transparent and electrically conductive film having a low electric resistance and a high transmittance and a method for making the film mentioned above. A mixture of inorganic indium compound and organic tin compound is combined with organic compound capable of coordinating with either of indium and tin to form an organic solution. When the mixture is heated, the inorganic indium compound and the organic tin compound coordinating partially with the organic compound react with water of crystallization of inorganic indium compound. The organic tin compound is partially subjected to hydrolysis to form an intermediate complex compound including indium and tin. This suppresses the evaporation of tin and generates a uniform film having a high transmittance and a low electric resistance. An addition of polyhydric alcohol increases the viscosity of the solution and gives a high stability to a resultant film obtained by applying the composition to the substrate and firing.

SPECIFICATION

This is a continuation application of application Ser. No. 08/252,389filed Jun. 1, 1994 which was a 37 C.F.R. Specification § 1.62 FWC ofSer. No. 07/916,722 filed Jul. 22, 1992, both applications nowabandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a composition for use in a transparentand electrically conductive film and a method for making the film andmore particularly to a composition for a transparent and electricallyconductive film formed on a glass substrate or a ceramic substrate and amethod for making the film.

Hitherto, an electrode material having a high transmittance for avisible light has been used in a display element such as a liquidcrystal display and an electroluminesence display and in a heatingresistor for preventing the window glass of a car, an air plane andbuilding from collecting moisture or from freezing.

There has been known a transparent and electrically conductive materialwhich usually consisted of antimony tin oxide(ATO) or indium tinoxide(ITO). These metal oxides can be applied to the glass substrate ora ceramic substrate for formation of a transparent and electricallyconductive film.

The transparent and electrically conductive film can be formed by thefollowing methods: (1) vacuum deposition method; (2) sputtering method;(3) CVD method; (4) screen printing method and (5) dipping method.

However, the above methods (1), (2) and (3) require a complicatedequipment in a high cost and have a problem in the cost and the massproduction. The methods (4) and (5) have a possibility to solve theproblem due to the methods (1), (2) and (3), but have difficulty to forma film superior in the practical use.

For example, a use of organic solution of an inorganic compound such asindium nitrate, indium chloride or stannic chloride causes the formedfilm to generate a white spot or to have a weak mechanical strengthwhich results in an easy scratching. There is a method to use an indiumorganic acid compound having a strong ion bonding such as indiumoctylate. Since the organic indium compound tends to be hydrolized andis relatively easy to be chemically changed, it is disadvantageous thatthe application method of liquid generates a gel state. Further, thereis proposed another method to use an organic complex of indium or tin.In this method, an evaporation of tin compound during the heat treatmentaccompanied with thermal decomposition of the film applied to the glasssubstrate prevents the resultant film from forming a uniform structure.It is difficult for this method to obtain a uniform film having a lowelectric resistance.

SUMMARY OF THE INVENTION

In order to solve the problem mentioned above, an object of the presentinvention is to provide a composition capable of forming a transparentand electrically conductive film having a low electric resistance and ahigh transmittance without the evaporation of tin compound during theheat treatment and a method for making the film by use of thecomposition.

As a result of our intensive study, we found that if a composition to beapplied on a substrate contains a tin compound in a complex formrepresented by the formula:

    InX.sub.p-r SnY.sub.q-s Z.sub.r+s,

the tin compound is not easy to evaporate during the heat treatment.Therefore, in a first aspect in order to achieve the object, the presentinvention is to provide a composition for use in a formation of atransparent and electrically conductive film, which comprises acomposite compound represented by the formula:

    InX.sub.p-r SnY.sub.q-s Z.sub.r+s

wherein InX_(p) is an inorganic indium salt, SnY_(q) is an organic tinsalt and Z is an organic compound capable of coordinating with indiumand tin; p, q, r and s are coordination numbers.

In accordance with a composition for use in a formation of transparentand electrically conductive film, a mixture of inorganic indium compoundand organic tin compound is combined with an organic compound capable ofcoordinating with both of indium and tin to form an organic solution.When the organic solution is heated, the inorganic indium compound andthe organic tin compound coordinating partially with the organiccompound react with water of crystallization of inorganic indiumcompound. The organic tin compound is partially hydrolyzed to form theintermediate complex compound including indium and tin as represented bythe above formula. This suppresses the evaporation of tin or tincompound and provides a uniform film having a high transmittance and alow electric resistance.

Accordingly, in a further aspect of the present invention, there isprovided a composition for use in a formation of a transparent andelectrically conductive film, which is prepared by partial hydrolysisunder heat treatment of an organic solution mainly containing aninorganic indium compound, an organic tin compound and an organiccompound capable of coordinating with indium and tin.

In the organic solution, said organic tin salt is preferably mixed withsaid inorganic indium salt in a mixing ratio of 5 to 20 wt % by adefinition of Sn/(Sn+In)×100%.

Further, it is preferred that said inorganic indium salt is selectedfrom the group consisting of indium nitrate, indium sulfate and indiumchloride. Also, it is preferred that said organic tin salt is selectedfrom the group consisting of salts of a carboxylic acid and adicarboxylic acid. Furthermore, it is preferred that said organiccompound capable of coordinating with tin and indium is selected fromthe group consisting of β-diketone group, α- or β-ketone acid group,ester group of α- or β-ketone acid group and α or β-amino alcohol group.

An addition of polyhydric alcohol increases the viscosity of the organicsolution and gives a high stability to a resultant film obtained byapplying the solution to the substrate and firing. Accordingly, in athird aspect of the present invention, there is provided a compositionfor use in a formation of a transparent and electrically conductive filmwhich further contains a polyhydric alcohol.

Since the composition for use in a formation of a transparent andelectrically conductive film is fixed on the substrate, it is preferredthat the composition further contains a catalyzer for thermaldecomposition in order to promote a thermal decomposition. The catalyzeris preferably selected from the group consisting of a peroxide compoundand a nitro compound. Preferred examples are hydrogen peroxide,tri-nitrotoluene and picric acid since these compounds having smallcarbon number tend to leave little residual carbon after the thermaldecomposition thereof.

In a fourth aspect of the present invention, there is provived a methodfor making a transparent and electrically conductive film, whichcomprises steps of providing a composition for use in a formation of atransparent and electrically conductive film by heating an organicsolution mainly comprising an inorganic indium salt, an organic tin saltand an organic compound capable of coordinating with indium and tin tocarry out partial hydrolysis of said organic solution and, if necessary,thereafter adding a polyhydric alcohol and/or a catalyzer for thermaldecomposition to the resultant organic solution; applying saidcomposition to a substrate and after drying subjecting the substratehaving said composition film applied thereto to a firing treatment.

In the method for making a transparent and electrically conductive film,it is preferred that the firing treatment is carried out in atemperature rising speed of 20° C./min. or more and under a pressurizedatmosphere of steam in order to promote a hydrolysis reaction.

In order to carry out the method for making a transparent andelectrically conductive film under a reducing atmosphere, it isnecessary that the organic tin salt has an oxygen content of 22 at % ormore. Even if the firing treatment is carried out under the reducingatmosphere, the organic compound capable of coordinating with both ofindium and tin can evaporate before the thermal decomposition thereofand the inorganic indium compound and the organic tin compound canthermally decompose by means of their own oxygen, so that the oxygendefect amount becomes increased and thus the resulting film resistancecan be lowered, comparing with that of a film formed by firing under aconventional oxygen atmosphere.

In the method for making a transparent and electrically conductive filmin order to achieve a uniform heating the composition applied on thesubstrate to prevent a formation of semi-hardened or cracked skin layeron a surface of the film, it is preferred that the firing treatment iscarried out by means of thermal decomposition due to a radiant heatunder a semi-closed atmosphere. Such a thermal decomposition under thesemi-closed atmosphere may be carried out in a room defined by wallsmade of metal, glass or ceramics material provided with small holes,whereby the atmosphere pressure can be self-controlled by means of aratio B/A between (B) an amount of decomposed gas generated upon thethermal decomposition of the composition applied on the substrate andthe (A) total area of the small holes for discharging the decomposedgas.

In an embodiment for carrying out the above method for making atransparent and electrically conductive film, an oven provided with thefollowing design conditions can realize the best mode of the thermaldecomposition:

(1) wherein the thermal decomposition under the semi-closed atmosphereis carried out in a room defined by walls, each of which temperature canbe controlled independently in a manner to make a property oftransparent and electrically conductive film formed on front and backsurfaces of the substrate to be uniform.

(2) wherein the thermal decomposition under the semi-closed atmosphereis carried out by a direct heat from the walls or by a indirect heat ina semi-closed box heated by a receiving heat from the walls.

(3) wherein the pressure of the semi-closed atmosphere is from 5 to 100mmH₂ O when the thermal decomposition is going.

(4) wherein a ratio (V/A) between the room volume (V) of the semi-closedatmosphere and the total area (A) of the holes for discharging thedecomposed gas is from 50 to 2000 cm³ /cm².

(5) wherein a ratio (B/A) between the amount (B) of the decomposed gasand the total area (A) of the holes for discharging the decomposed gasis from 100 to 10000 ml/cm³.

(6) wherein a ratio (B/V) between the amount (B) of the decomposed gasand the room volume (V) of the semi-closed atmosphere is from 0.01 to1000 ml/cm³.

Meanwhile, according to the method of the present invention, there areprovided various kinds of the transparent and electrically conductivefilms. Among them, as a result of our studying a relation between theaverage particle size and the electrical resistance or the visible lighttransmittance (at 550 nm), we found that the films which comprise oxideparticles of indium and tin having a particle diameter of 30 to 100 nmare superior in the electrical resistance as shown in FIG.2, since aparticle size of 100 nm or more makes a contact resistance between theparticles to be large and thus results in a lower packing density. Onthe contrary, a particle size of 30 nm or less makes a film strength tobe weak and thus makes a film resistance to be large.

Also, we found that the more uniform the avarage particle size becomes,the higher strength the film is provided with. Accordingly, the presentinvention is to provide a transparent and electrically conductive film,wherein 90% of the oxide particles is within a distribution of centerparticle size ±3σ, whereby the film comes to have a much lowerresistance.

Further, as a result of studying the relation between the averageparticle size and the film thickness, we found that it is preferablethat a ratio a/b between the average particle size (a) and the filmthickness (b) is 0.7 or less, because the number of particles arrangedin a series to a thickness direction of the film has the substantialinfluence on the film strength.

BRIEF DESCRIPTION OF THE DRAWING

FIG.1 is a graph showing a relationship between a sheet electricresistance and a ratio Sn/(Sn+In)×100%.

FIG.2 is a graph showing a relationship between an average particle sizeof a transparent and electrically conductive film, and an electricalresistance and a visible light transmittance of the film.

FIG.3 is a schematic diagram of an electric furnace used for carryingout a method of preparing a transparent and electrical conductive filmaccording to the present invention.

FIG.4 is a schematic diagram of another electric furnace.

FIG.5 is a schematic diagram of a box used for providing an atmospherefor thermal decomposition.

FIG.6 is a schematic diagram of a tunnel type electric furnace forheating a box of FIG.5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the accompanying drawings, the description will be directedto a preferred embodiment of a composition for use in a formation of atransparent and electrically conductive film and a method for making thefilm.

A composition for use in a formation of a transparent and electricallyconductive film according to the present invention is synthesized in thefollowing way:

First, inorganic indium compound InXp is mixed with an organic compoundZ capable of coordinating with both of tin and indium. The inorganicindium compound may be composed of a material which has a ligandexchangeable with the organic compound capable of coordinating withindium and tin. For example, the inorganic indium compound may becomposed of indium nitrate, indium sulfate or indium chloride,preferably including water of crystallization. The organic compoundcapable of coordinating with both of indium and tin is able tocoordinate partially with indium and tin and to promote a formation ofan intermediate compound of indium and tin as represented by theformula:

    InX.sub.p-r SnY.sub.q-s Z.sub.r+s.

Further, the organic compound is required to have a solubility in anorganic solvent and may be composed of β-diketone group, α- or β-ketoneacid group, ester group of α- or β-ketone acid group or α- or β-aminoalcohol group. Examples of β-diketone group are acetyl acetone, methylacetyl acetone, acetoacetic ethyl ester, acetyl methyl ethyl ketone,trifluoro-acetyl acetone, malonic-acid diethyl ester, dibenzoyl acetone,benzoyl methane, benzoyl-trifluoro acetone, furoyl acetone,2-furoylbenzoyl acetone, 2-thenoyl acetone and a mixture thereof.Examples of α- or β-ketone acid groups are acetoacetic acid, propionylbutyric acid, benzoyl acetic acid, acetyl formic acid, benzoyl formicacid and the like. Examples of the ester group of α- or β-ketone acidgroups are methyl, ethyl, propyl, butyl esters thereof. Examples of α-or β-amino alcohol groups are amino ethylalcohol and the like.

To the solution is added an organic solvent and an organic tin compoundSnYq and the resulting solution is heated. The organic tin compound israther stable in air but is easily hydrolyzed by heating. For example,available material as the organic tin compound is tin carboxylate or tindicarboxylate and preferably tin formate, tin acetate or tin oxalatewhich has a small number of carbon atoms.

The organic solvent may be composed of a solvent capable of dissolvingthe organic compound and inorganic compound used in this embodiment.Available solvent is, for example, an aromatic hydrocarbon group such astoluene, xylene; alcohol group such as ethanol and isopropanol; aceticester group such as ethyl acetate, butyl acetate; ketone group such asacetone and methylethyl ketone and diethyl ketone; ether group such asmethoxyl-ethanol and ethoxyl-ethanol and tetrahydrofuran. The heatingtemperature of the organic solution is preferably a temperature equal toor close to a reflux temperature of the organic solution includinginorganic indium compound, organic tin compound and organic compoundcapable of coordinating with indium and tin.

After being heated, the organic solution is cooled to a room temperatureand a polyhydric alcohol is added to the solution group to form acomposition for use in a formation of a transparent and electricallyconductive film. The addition of polyhydric alcohol is to increaseviscosity of the organic solution and to promote the stability of theresultant film obtained by applying the organic solution to thesubstrate, and drying. For example, possible alcohol may contain aglycol group and trivalent alcohol and is preferably ethylene glycol orglycerol which leaves hardly any residual carbon during thermaldecomposition.

The composition for use in formation of transparent and electricallyconductive film is applied to a substrate, dried and fired to form aresultant transparent and electrically conductive film. Availableapplication method is a screen printing method, a roll coating method, adip coating method and a spin coating method and preferably is a dipcoating method or a spin coating method. A firing temperature is a rangehigher than the decomposition temperature of the composition and lowerthan the deformation temperature of substrate and preferably ranges from400° to 700° C.

The following description will be directed to the preferred embodiment.However, the scope of the present invention is not limited to thepreferred embodiment.

EXAMPLE 1

A mixture of 45 g of indium nitrate (In(NO₃)₃ ·3H₂ O) and 50 g of acetylacetone is put in an 1 l Erlenmeyer flask and stirred and dissolved atroom temperature to form a solution. The solution has 0 g, 1.35 g, 2.7g, 4.05 g, 5.4 g, and 8.1 g of stannous oxalate (tin oxalate) addedthereto in order to make a tin ratio, 0, 5, 10, 15, 20 and 30 wt % inrespect to Sn/(Sn+In)×100%, wherein Sn is an amount contained instannous oxalate and In is an amount contained in indium nitrate.Further, the solution has acetone added thereto and is refluxed. Then,the solution has 10 g of glycerol added thereto and is stirred and mixedto synthesize a composition for use in a formation of a transparent andelectrically conductive film. A glass plate having SiO₂ film appliedthereto is dipped into the solution and is withdrawn at a rate of 60cm/min from the solution. Then, the glass plate is kept at roomtemperature for 5 min. After being dried at 100° C. for 5 min, the filmapplied to the glass plate is fired at 500° C. for one hour in air toform a transparent and electrically conductive film. The resultant filmis of a thickness of 0.05 micron and its electric characteristic isshown in FIG. 1.

As shown in FIG. 1, when a mixing ratio of indium nitrate to stannousoxalate is equivalent to 5 to 20 wt % of Sn/(Sn+In)×100, the film has alow electric sheet resistance (Ω/□)

EXAMPLE 2

The inorganic indium compound is composed of indium chloride (InCl₃ ·3H₂O) and the organic tin compound is composed of stannous oxalate. Amixing ratio of indium chloride and stannous oxalate is arranged to be10 wt % in respect to Sn/(Sn+In)×100%. Other conditions are similar tothose of Example 1.

EXAMPLE 3

The organic tin compound is composed of stannous acetate (Sn (CH₃COO)₂). A mixing ratio of indium nitrate and stannous acetate isarranged to be 10 wt % in respect to Sn/(Sn+In)×100%. Other conditionsare similar to those of Example 1.

EXAMPLE 4

The organic compound capable of coordinating with indium and tin iscomposed of 2-amino alcohol. Other conditions are similar to those ofExample 1.

EXAMPLE 5

The polyhydric alcohol is composed of ethylene glycol. Other conditionsare similar to those of Example 1.

Comparative Example 1

A mixture of 45 g of indium nitrate and 5.4 g of stannic chloride (SnCl₄·5H₂ O) is prepared in a way that the ratio of Sn/(Sn+In) is 10 wt % andhas acetone added therein. The mixture ×100% is stirred and mixed toform a composition for use in a formation of transparent andelectrically conductive film. A glass plate having SiO₂ film appliedthereto is dipped into the composition and is withdrawn at a rate of 60cm/min from the solution. Then, the glass plate is kept at roomtemperature for 5 min. After being dried at 100° C. for 5 min, thesolution applied to the glass is fired at 500° C. for one hour in air toform a transparent and electrically conductive film.

Table 1 shows testing results obtained with Examples 2 to 5 andComparative Example 1.

                  TABLE 11                                                        ______________________________________                                              Film    Sheet                                                                 Thick   Resis                                                                 ness    tance   Transmittance    surface                                      (μm) (Ω/□)                                                                (%) at 550 nm                                                                           Adhesion                                                                             Hardness                               ______________________________________                                        Ex. 2 0.05     500    87        good   good                                   Ex. 3 0.05     550    87        good   good                                   Ex. 4 0.06     400    86        good   good                                   Ex. 5 0.04     600    88        good   good                                   Com. 1                                                                              0.03    4000    Cloudy    poor   poor                                   ______________________________________                                    

In view of the above embodiment, it is clear that the composition foruse in a formation of transparent and electrically conductive film andthe method for forming the film according to the present invention, makeit possible to manufacture the transparent and electrically conductivefilm easily and at a low cost and is suitable for a transparentelectrode such as a display device or a heating resistor.

EXAMPLE 6

A mixture of 45 g of indium nitrate (In(NO₃)₃ ·2H₂ O) and 50 g of acetylacetone is put in an 1 l Erlenmeyer flask and stirred and dissolved atroom temperature to form a solution. The solution has 5.4 g of stannousoxalate (oxygen content of 57 at %) added thereto in order to make a tinratio, 10 wt % in respect to Sn/(Sn+In)×100%. Further, the solution hasacetone added thereto and is refluxed. Then, the solution is stirred andmixed to synthesize a composition for use in a formation of atransparent and electrically conductive film. A glass plate having SiO₂film applied thereto is dipped into the solution and is withdrawn at arate of 60 cm/min from the solution. Then, the glass plate is kept atroom temperature for 5 min. After being dried at 100° C. for 5 min, thefilm applied to the glass plate is fired at 500° C. for one hour in N₂to form a transparent and electrically conductive film.

EXAMPLE 7

The inorganic indium compound is composed of indium sulfate (In₂ (SO₄)₃·9H₂ O) and the organic tin compound is composed of stannous oxalate. Amixing ratio of indium chloride and stannous oxalate is arranged to be10 wt % in respect to Sn/(Sn+In)×100%. Other conditions are similar tothose of Example 6.

EXAMPLE 8

The organic tin compound is composed of stannous glutarate (SnC₅ H₆ O₄)having an oxygen content of 25 at %. A mixing ratio of indium nitrateand stannous glutarate is arranged to be 10 wt % in respect toSn/(Sn+In)×100%. Other conditions are similar to those of Example 6.

EXAMPLE 9

The organic compound capable of coordinating with indium and tin iscomposed of 2-aminoethylalcohol (H₂ NC₂ H₅ OH). Other conditions aresimilar to those of Example 6.

EXAMPLE 10

The atmosphere gas is composed of argon. Other conditions are similar tothose of Example 6.

Comparative Example 2

The organic tin compound is composed of stannous adipate (SnC₆ H₈ O₄)having an oxygen content of 21 at %. and is arranged to be 10 wt % inrespect to Sn/(Sn+In)×100%. Other conditions are similar to those ofComparative Example 1.

Table 2 shows testing results obtained with Examples 6 to 10 andComparative Examples 1 and 2.

                  TABLE 2                                                         ______________________________________                                              Film    Sheet                                                                 Thick   Resis                                                                 ness    tance   Transmittance    surface                                      (μm) (Ω/□)                                                                (%) at 550 nm                                                                           Adhesion                                                                             Hardness                               ______________________________________                                        Ex. 6 0.06     250    85        good   good                                   Ex. 7 0.06     260    85        good   good                                   Ex. 8 0.06     270    85        good   good                                   Ex. 9 0.07     210    84        good   good                                   Ex. 10                                                                              0.06     250    85        good   good                                   Com. 1                                                                              0.06    4000    Cloudy    poor   poor                                   Com. 2                                                                              0.06    1000    78        good   poor                                   ______________________________________                                    

In view of the above embodiment, it is clear that the composition foruse in a formation of transparent and electrically conductive filmaccording to the present invention makes it possible to manufacture thetransparent and electrically conductive film easily and at a low costand is suitable for a transparent electrode such as a display device ora heating resistor.

EXAMPLE 11

A mixture of 45 g of indium nitrate (In(NO₃)₃ ·3H₂ O) and 50 g of acetylacetone is put in an 1 l Erlenmeyer flask and stirred and dissolved atroom temperature to form a solution. The solution has 5.4 g of stannousoxalate (SNC₂ O₄) added thereto in order to make a tin ratio to 10 wt %in respect to Sn/(Sn+In)×100%. Further, the solution has acetone addedthereto and is refluxed. After reflux, the solution is cooled to a roomtemperature. Then, 0.1 g of hydrogen peroxide is added thereto and thesolution is stirred and mixed to synthesize a composition for use in aformation of a transparent and electrically conductive film. A glassplate having SiO₂ film applied thereto is dipped into the solution andis withdrawn at a rate of 60 cm/min from the solution. Then, the glassplate is kept at room temperature for 5 min. After being dried at 100°C. for 5 min, the film applied to the glass plate is fired at 500° C.for one hour in air to form a transparent and electrically conductivefilm. The resultant film is of a thickness of 0.05 micron.

EXAMPLE 12

The inorganic indium compound is composed of indium chloride (InCl₃ ·3H₂O) and the organic tin compound is composed of stannous oxalate. Amixing ratio of indium chloride and stannous oxalate is arranged to be10 wt % in respect to Sn/(Sn+In)×100%. Other conditions are similar tothose of Example 11.

EXAMPLE 13

The organic tin compound is composed of stannous acetate (Sn (CH₃COO)₂). A mixing ratio of indium nitrate and stannous acetate isarranged to be 10 wt % in respect to Sn/(Sn+In)×100%. Other conditionsare similar to those of Example 11.

EXAMPLE 14

The organic compound capable of coordinating with indium and tin iscomposed of 2-amino alcohol. Other conditions are similar to those ofExample 11.

EXAMPLE 15

The catalyzer for thermal decomposition is composed of 1 g oftri-nitrotoluene. Other conditions are similar to those of Example 11.

Table 3 shows testing results obtained with Examples 11 to 15 andComparative Example 1.

                  TABLE 3                                                         ______________________________________                                              Film    Sheet                                                                 Thick   Resis                                                                 ness    tance   Transmittance    surface                                      (μm) (Ω/□)                                                                (%) at 550 nm                                                                           Adhesion                                                                             Hardness                               ______________________________________                                        Ex. 11                                                                              0.03     660    88        good   good                                   Ex. 12                                                                              0.03     700    88        good   good                                   Ex. 13                                                                              0.03     720    88        good   good                                   Ex. 14                                                                              0.04     520    87        good   good                                   Ex. 15                                                                              0.04     500    87        good   good                                   Com. 1                                                                              0.03    4000    Cloudy    poor   poor                                   ______________________________________                                    

In view of the above embodiment, it is clear that the composition foruse in a formation of transparent and electrically conductive filmaccording to the present invention makes it possible to manufacture afilm the superior in electrical conductivity and transparency in avisible light region easily and at a low cost and is suitable for atransparent electrode such as a display device or a heating resistor.

EXAMPLE 16

A mixture of 60 g of indium nitrate (In(NO₃)₃ ·3H₂ O) and 50 g of acetylacetone is put in an 1 l Erlenmeyer flask and stirred and dissolved atroom temperature to form a solution. The solution has 10 g of stannousoxalate (SnC₂ O₄) and acetone added thereto and is refluxed. Then, thesolution has 10 g of glycerol added thereto and is stirred and mixed tosynthesize a composition for use in a formation of a transparent andelectrically conductive film. A glass plate having SiO₂ film appliedthereto is dipped into the solution and is withdrawn at a rate of 60cm/min from the solution. Then, the glass plate is kept at roomtemperature for 5 min. After being dried at 100° C. for 5 min, the filmapplied to the glass plate is sintered at 500° C. under a pressurizedsteam atmosphere for one hour in air to form a transparent andelectrically conductive film. The temperature rising speed is 20°C./min. The resultant film is of a thickness of 0.07 micron.

EXAMPLE 17

The method of Example 16 is carried out at the rising speed of 30°C./min.

EXAMPLE 18

The method of Example 16 is carried out at the rising speed of 50°C./min.

Comparative Example 3

A mixture of 50 g of indium nitrate, 6.0 g of stannic chloride (SnCl₄·5H₂ O) and acetone is stirred and mixed to form a composition for usein a formation of transparent and electrically conductive film. A glassplate having SiO₂ film applied thereto is dipped into the compositionand is withdrawn at a rate of 60 cm/min from the solution. Then, theglass plate is kept at room temperature for 5 min. After being dried at100° C. for 5 min, the solution applied to the glass is fired at 500° C.for one hour in air to form a transparent and electrically conductivefilm.

Table 4 shows testing results obtained with Examples 16 to 18 andComparative Example 3.

                  TABLE 4                                                         ______________________________________                                              Film    Sheet             Average                                             Thick   Resis             particle                                            ness    tance   Transmittance                                                                           size                                                (μm) (Ω/□)                                                                (%) at 550 nm                                                                           (nm)   Adhesion                               ______________________________________                                        Ex. 16                                                                              0.07     200    85        30     good                                   Ex. 17                                                                              0.07     300    85        35     good                                   Ex. 18                                                                              0.07     400    85        40     good                                   Com. 3                                                                              0.05    2000    50        50     poor                                   ______________________________________                                    

In view of the above embodiment, it is clear that the films according tothe present invention come to have a uniform size distribution of 30 to100 nm and result in superior electrical conductance and a transparencyin a visible light region, so that the film is suitable for atransparent electrode such as a display device or a heating resistor.

EXAMPLE 19

A mixture of 45 g of indium nitrate (In(NO₃)₃ ·3H₂ O) and 50 g of acetylacetone is put in an 1 l Erlenmeyer flask and stirred and dissolved atroom temperature to form a solution. The solution has 0 to 8.1 g ofstannous oxalate (SnC₂ O₄) added thereto in order to make a tin ratio of0 to 30 wt % in respect to Sn/(Sn+In)×100%, wherein Sn is an amountcontained in stannous oxalate and In is an amount contained in indiumnitrate. Further, the solution has acetone added thereto and isrefluxed. Then, the solution after reflux is cooled to a roomtemperature and has 10 g of glycerol added thereto and is stirred andmixed to synthesize a composition for use in a formation of atransparent and electrically conductive film. A glass plate having SiO₂film applied thereto is dipped into the solution and is withdrawn at arate of 60 cm/min from the solution. Then, the glass substrate is keptat room temperature for 5 min. After being dried at 100° C. for 5 min,the substrate 2 provided with the film is placed in a room 1 of anelectric furnace as shown in FIG. 3 and is heated at a temperaturerising speed of 30° C. from a room temperature to 500° C. and is kept at500° C. for one hour in air to form a transparent and electricallyconductive film.

In the example, the electric furnace is made of stainless steel having10 mm in a thickness and a temperature sensor 5 and an electric neater 4are provided at a bottom 3 of the electric furnace and are connected toa temperature control circuit 6 in order to control a temperature of theinner room. Any heater is not provided at sides 7 and 8 and a lid 9. Thelid is provided with small holes communicating the inner room to anouter thereof, which is designed in a way to adjust a gas pressure inthe furnace room 1 within 5 to 100 mmH₂ O by means of gas generating onthe thermal decomposition.

EXAMPLE 20

In the Example 19, the substrate is placed and kept for 30 minutes in aroom of the electric furnace preheated at 500° C.

EXAMPLE 21

As shown in FIG. 4, an electric oven similar to Example 1 is furtherprovided with an electric heater 14 and a temperature sensor 16 at a lid12 of the room 1, which are connected with a temperature control circuit18. At a bottom 11 of the room, the electric heater 13 and temperaturesensor 15 is provided in a similar manner to Example 1, which areconnected to a temperature control circuit 17. The lid 12 has smallholes 10 which communicate the inner room to an outer thereof.

In the electric furnace, temperatures of each of the furnace walls isindependently controlled in a way to elevate temperatures of front andback surfaces of the substrate 2 in a same pattern.

EXAMPLE 22

As shown in FIG. 5, a substrate 25 provided with a same composition asExample 19 is placed in an aluminum box 22 provided with small holes 21at a lid thereof, which box is continuously transferred through a tunneltype furnace and heated by a heater 24 as shown in FIG. 6. The maximumattainable temperature is 500° C. and the heating time is about 20minutes.

EXAMPLE 23

A mixture of 45 g of indium nitrate (In(NO₃)₃ ·3H₂ O) and 5.4 g ofstannous chloride (SnCl₄ ·5H₂ O) and acetone is put in an 1 l Erlenmeyerflask and stirred and mixed to form a composition for use in a formationof a transparent and electrically conductive film. A glass plate havingSiO₂ film applied thereto is dipped into the solution and is withdrawnat a rate of 60 cm/min from the solution. Then, the glass substrate iskept at room temperature for 5 min. After being dried at 100° C. for 5min, the substrate is subjected to a same firing treatment as Example20.

Comparative Example 4

The same composition as Example 19 is applied on a substrate by adipping method and the substrate is kept at 500° C. for one hour in anelectric furnace wherein convective heat transfer mainly occurs, toobtain a transparent and electrical conductive film.

Comparative Example 5

The same composition as Example 23 is applied on a substrate by adipping method and the substrate is subjected to a same treatment forthermal decomposition as the above Comparative Example 4.

Table 5 shows testing results obtained with Examples 19 to 23 andComparative Examples 4 and 5. All films thus obtained are 50 nm in athickness.

                  TABLE 5                                                         ______________________________________                                                                                Differ-                                                                       ence be-                                                                      tween                                                 Sheet                   front and                                             Resis-  Transmit-       back re-                                              tance   tance (%)       sis-                                        Cracking  (Ω/□)                                                                at 550 nm                                                                             Adhesion                                                                              tance(%)                              ______________________________________                                        Ex.19 NONE       400    87      good     3                                    Ex.20 NONE       400    87      good     3                                    Ex.21 NONE       400    88      good     0                                    Ex.22 NONE       400    88      good     1                                    Ex.23 NONE       500    86      good     5                                    Com.4 SOME       500    85      normal  10                                    Com.5 MANY      4000    Cloudy  bad     20                                    ______________________________________                                    

In view of the above embodiment, it is understood that control of areaction pressure needs the optimum gas pressure of atmosphere and it isclear that an a furnace provided with the following design conditionscan realize the best mode of the thermal decomposition:

(1) that the pressure of the semi-closed atmosphere is from 5 to 100mmH₂ O when the thermal decomposition is going.

(2) that a ratio (V/A) between the room volume (V) of the semi-closedatmosphere and the total area (A) of the holes for discharging thedecomposed gas is from 50 to 2000 cm³ /cm².

(3) that a ratio (B/A) between the amount (B) of the decomposed gas andthe total area (A) of the holes for discharging the decomposed gas isfrom 100 to 10000 ml/cm³.

(4) that a ratio (B/V) between the amount (B) of the decomposed gas andthe room volume (v) of the semi-closed atmosphere is from 0.01 to 1000ml/cm³.

In the composition for use in a formation of a transparent andelectrically conductive, it is preferable that said organic tin salt ismixed with said inorganic indium salt in a mixing ratio of 5 to 20 wt %by a definition of Sn/(Sn+In) ×100%.

In the embodiment for forming a transparent and conductive film by meansof radiant heating, the pressurizing is carried out under thesemi-closed atmosphere. In the place of this method, the pressurizingmay be carried out at a pressure higher than atmosphere by means ofpressure device. Also, the radiant heating may be carried out in anatmosphere without pressurizing. Further, the method may be carried outat a pressure higher than atmosphere by means of convective heating.

While the box for heating the composition for forming a transparent andconductive film is made of alumina in Example 22, it may be made of anyother materials having a same function such as ceramics, metal, glassand the like.

While the walls of the furnace is made of stainless steel in the aboveExample, it may be made of ceramics and glass materials.

The method according to the embodiment of the present invention issuitable to a method for forming a transparent and conductive film onboth sides of a transparent substrate such as glass substrate and thelike, so that the method can be used for making a EL touch panel and thelike.

While the embodiment is carried out by the radiant heating, the heatingby conduction may be used for forming a transparent and conductive filmon a single surface of a substrate.

Therefore, according to the present invention there is obtained atransparent and conductive film provided with no cracking, superiortransmittance, much uniform characteristics, so that the resultingelectrode comes to have a low resistance and a higher transmittance.

What is claimed is:
 1. A composition for use in a formation of atransparent and electrically conductive film, which comprises a compoundrepresented by the formula:

    InX.sub.p-r SnY.sub.q-s Z.sub.r+s

wherein: InX_(p) is an inorganic indium salt; SnY_(g) is an organic tinsalt of a dicarboxylic acid or formic acid; Z is an organic compoundcapable of coordinating with indium and tin, which is selected from thegroup consisting of β-diketone group, α- or β-ketone acid group, estergroup of α- or β-ketone acid group and α- or β-amino alcohol group; and,p, q, r and s are coordination numbers.
 2. The composition for use in aformation of a transparent and electrically conductive film according toclaim 1, which is prepared by partial hydrolysis under heat treatment ofan organic solution comprising an inorganic indium salt, an organic tinsalt and an organic compound capable of coordinating with indium andtin.
 3. The composition for use in a formation of a transparent andelectrically conductive film according to claim 1, wherein said organictin salt is mixed with said inorganic indium salt in a mixing ratio of 5to 20 wt % by a definition of Sn/(Sn+In)×100%, wherein Sn is an amountcontained in the organic tin salt and In is an amount contained in theinorganic indium salt.
 4. The composition for use in a formation of atransparent and electrically conductive film according to claim 1,wherein said inorganic indium salt is selected from the group consistingof indium nitrate, indium sulfate and indium chloride.
 5. Thecomposition for use in a formation of a transparent and electricallyconductive film according to claim 1, which further comprises apolyhydric alcohol.
 6. The composition for use in a formation of atransparent and electrically conductive film according to claim 1, whichfurther comprises a catalyzer for thermal decomposition.
 7. Thecomposition for use in a formation of a transparent and electricallyconductive film according to claim 6, wherein the catalyzer is selectedfrom the group consisting of a peroxide compound and a nitro compound.8. A composition for use in a formation of a transparent andelectrically conductive film, which consists essentially of a compoundrepresented by the formula:

    InX.sub.p-r SnY.sub.q-s Z.sub.r+s

wherein: InX_(p) is an inorganic indium salt; SnY_(q) is an organic tinsalt of a dicarboxylic acid or formic acid; Z is an organic compoundcapable of coordinating with indium and tin, which is selected from thegroup consisting of β-diketone group, α- or β-ketone acid group, estergroup of α- or β-ketone acid group and α- or β-amino alcohol group; and,p, q, r and s are coordination numbers.